Planarian regeneration serves as a platform to study how animals can precisely restore their missing body parts after injury. The planarian Dugesia japonica can regenerate a complete individual even from a tiny tail fragment via activation of somatic pluripotent stem cells called neoblasts. We found that interplay between anterior extracellular signal-related kinase (ERK) signaling and posterior b-catenin signaling can account for the reconstruction of a complete head-to-tail axis after amputation. Furthermore, our data suggest that the balance between anterior ERK signaling and posterior b-catenin signaling may vary among planarian species, resulting in the drastic differences of the head-regenerative ability of their tail fragments. We demonstrated that RNA interference of the b-catenin gene enabled de novo regeneration of a functional head from head non-regenerative tail fragments of the planarian Phagocata kawakatsui.